1. Field of the Invention
This invention relates to oil-soluble overbased trace metal naphthenates and to their use as micronutrients. In one of its aspects, the invention relates to the preparation of overbased metal naphthenate spray oil solutions which possess increased proportions of the metal while remaining non-phytotoxic. In another, the invention is concerned with the use of such compositions for foliar feeding.
Certain elements are required by plants in very small quantities for their proper nutrition. These so-called trace elements (also referred to as minor- or micro-elements) include copper, iron, manganese, molybdenum and zinc. Trace elements deficiencies in plants are widespread and often occur in soils which contain adequate quantities of the element but in a form unavailable to the plant. The shortage of one or more of these elements usually affects the plant appearance and its productivity, giving rise to typical growth symptoms. Trace element deficiencies are widespread in citrus-growing areas. In Trinidad, zinc and manganese are probably the most encountered nutrient disorders in citrus, and in Jamaica copper, iron, zinc and manganese deficiencies are quite common, while zinc and manganese deficiencies are the chief limiting factor in British Honduras.
A non-phytotoxic spray oil is believed more effective than the conventional aqueous medium for foliar micronutrient sprays; absorption through the leaf cuticle via the wax canals is more rapid and the oil solution is more resistant to weathering. Furthermore, the metal is presented in a non-ionic form.
2. Description of the Prior Art
The prior art to which this invention relates is aware, inter alia of U.S. Pat. Nos. 3,661,550 and 2,865,956. Reference is made to coassigned U.S. Pat. No. 3,661,550 which discloses oil-soluble but neutral metal naphthenate micronutrient compositions. While these are generally effective, they tend to cause burns on the surface of leaves, probably due to the presence of free naphthenic acids.
U.S. Pat. No. 2,869,956 describes naphthenates made by a carbonation method so that their overbasicity is due to the metal carbonate moiety of the naphthenate in the inner core of the micelle. The empirical formula which expresses this type of overbased metal naphthenate is MR.sub.2.xMCO.sub.3. The direct carbonation method for making 800% overbased metal naphthenate can be represented by the overall equation: ##EQU1## where RCOOH represents naphthenic acid, M is the metal and x is the number of metal naphthenate molecules in the outer layer of the micelle. We have not been able to make overbased naphthenates of the trace elements copper, iron, manganese, molybdenum and zinc by direct carbonation as described in U.S. Pat. No. 2,865,956.